Hardfacing for progressing cavity pump rotors

Abstract

A hardfacing for downhole progressing cavity pumps is disclosed as well as a method for producing same. The hardfacing consists of a metal carbide layer applied to the ferrous pump rotor body by way of plasma spraying and a top layer of metallic material having a lower hardness than the metal carbide. The metal carbide layer has a grainy surface with a plurality of peaks and intermediate depressions, the peaks being formed by metal carbide grains at the surface of the metal carbide layer. The thickness of the top layer is adjusted such that the depressions between the peaks of the metal carbide layer are completely filled thereby providing the rotor with a metal carbide hardfacing of significantly reduced surface roughness. In the process of the invention, the pump rotor, which may be provided with a molybdenum bonding layer, is plasma coated with the metal carbide and the resulting carbide layer is covered with the metallic material top layer. The top layer is polished either until the dimensions thereof are within the tolerances acceptable for the finished rotor or until a majority of the peaks of the carbide layer are exposed. The hardfacing significantly increases the service life of the rotor and stator of downhole progressing cavity pumps.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A pump rotor for a progressing cavity pump, comprising a rotor body made of a ferrous metal;   a layer of a metal carbide plasma sprayed onto the body, the metal carbide layer having a grainy surface with a plurality of peaks and intermediate depressions, the peaks being formed by metal carbide grains at the surface of the metal carbide layer; and   a top layer of metallic material bonded to the metal carbide layer, the thickness of the top layer being adjusted such that the depressions between the peaks of the metal carbide layer are completely filled while a majority of the peaks are exposed at the surface of the rotor, thereby providing the rotor with a metal carbide hardfacing of significantly reduced surface roughness.   
     
     
       2. The pump rotor as defined in claim 1, wherein the metal carbide is selected from the group consisting of carbides of tungsten, titanium, tantalum, columbium, vanadium, and molybdenum, and the metallic material of the top layer is selected from the group consisting of chromium, molybdenum and nickel and alloys thereof. 
     
     
       3. A pump rotor as defined in claim 1, wherein the metallic material of the top layer is selected from the group consisting of chrome/molybdenum and nickel/chromium alloys. 
     
     
       4. A pump rotor as defined in claim 1, wherein the metal carbide is tungsten carbide. 
     
     
       5. A pump rotor as defined in claim 1, wherein the body is made of stainless steel, the metal carbide is tungsten carbide, and the metal alloy is nickel/chromium. 
     
     
       6. A pump rotor as defined in claim 1, wherein the grain size of the tungsten carbide material sprayed onto the rotor body is 7.8 to 44 micrometer. 
     
     
       7. A downhole progressing cavity pump, comprising a stator made of elastomeric material; and   a pump rotor as defined in claim 1.   
     
     
       8. The pump rotor as defined in claim 1, wherein the rotor body has dimensions smaller than dimensions selected for the rotor and the metal carbide layer is applied to such a thickness that the diameter of the coated rotor body is within the selected dimensions. 
     
     
       9. The pump rotor as defined in claim 1, further including a bonding layer of molybdenum on the ferrous metal rotor body and under the metal carbide layer.